Wireless communication involves transmission of encoded information on a modulated radio frequency (RF) carrier signal. In a multi-carrier wireless communication system, such as an OFDM system, transmitted signals are susceptible to multi-path scattering and reflection, which can cause interference between information transmitted on different channels. For this reason, OFDM receivers typically include a channel estimator that measures fluctuation of the channel response. The receiver uses the measured channel response to adjust the detection of incoming signals, and thereby compensate for channel effects that could otherwise cause interference.
According to the IEEE 802.11a standard, fluctuation of the channel response that acts on a specific frequency bin is estimated using a number of known, repeatedly transmitted preamble symbols, or “tones.” For example, an IEEE 802.11a receiver estimates channel fluctuation in a given frequency bin by comparing the received (complex) amplitudes of the tone with the known amplitude of the preamble tone transmitted twice for a particular frequency bin. The estimated amount of channel fluctuation then is compensated by dividing the received value of the tone by the estimated gain term before the detector processes each tone. This operation is known as frequency domain equalization.